1. Field of the Invention
The invention relates to radioactive therapeutic seeds. More particularly, the invention relates to improved radioactive therapeutic seeds for the treatment of oncological and other medical conditions.
2. State of the Art
Radioactive seed therapy is a well known and well accepted medical procedure for the treatment of various oncological and other medical conditions. Seed therapy, also known as brachytherapy typically involves the implantation of one or more tiny capsules (seeds) into or around a treatment site. The capsules contain a radioactive isotope that irradiates the treatment site at close range without adversely affecting other parts of the body. Brachytherapy has been used successfully in the treatment of various types of cancers such as prostate cancer. It has also been used to prevent the growth or regrowth of tissues in the treatment of various occlusive diseases such as arteriosclerosis and arthrosclerosis subsequent to balloon angioplasty.
Radioactive therapeutic seeds are carefully designed to possess several important qualities. First, they are relatively small, typically approximately 0.025 inch in diameter and approximately 0.16 inch long, so that they may be implanted using minimally invasive instruments and techniques. Second, the radioactive isotope must be enclosed in a biocompatible protective package since the seeds are typically not removed and will remain in the body for many years. Third, the isotope should be positioned within the protective package so as to avoid any xe2x80x9chot spotsxe2x80x9d of radiation. Fourth, each seed preferably includes a radiopaque (e.g. high Z material) marker so that it can be located at the treatment site with the aid of fluoroscopy. Fifth, the protective package and the radiopaque marker are preferably configured such that each does not cast xe2x80x9cshadowsxe2x80x9d in the irradiation pattern of the isotope.
The state of the art of radioactive therapeutic seeds is substantially disclosed in seven U.S. Patents: No. 5,713,828 to Coniglione for xe2x80x9cHollow-Tube Brachytherapy Devicexe2x80x9d, No. 5,405,309 to Carden, Jr. for xe2x80x9cX-Ray Emitting Interstitial Implantsxe2x80x9d, No. 4,891,165 to Suthanthiran for xe2x80x9cDevice and Method for Encapsulating Radioactive Materialsxe2x80x9d and No. 4,784,116 to Russell, Jr. et al. for xe2x80x9cCapsule for Interstitial Implantsxe2x80x9d, No. 4,702,228 to Russell, Jr. et al. for xe2x80x9cX-Ray Emitting Interstitial Implantsxe2x80x9d, No. 4,323,055 to Kubiatowicz for xe2x80x9cRadioactive Iodine Seedxe2x80x9d, and No. 3,351,049 to Lawrence for xe2x80x9cTherapeutic Metal Seed Containing within a Radioactive Isotope Disposed on a Carrier and Method of Manufacturexe2x80x9d.
The Lawrence patent describes many of the essential features of radioactive therapeutic seeds. Lawrence describes radioactive isotopes (I-125, Pd-103, Cs-131, Xe-133, and Yt-169) which emit low energy X-rays and which have relatively short half-lives. Once implanted at a treatment site, these isotopes provide sufficient radiotherapy without posing a radiation danger to the medical practitioner(s), people in the vicinity of the patient, or other parts of the patient""s body. Lawrence further describes a protective capsule which contains the isotope and prevents it from migrating throughout the body where it might interfere with healthy tissue. The capsule is cylindrical and made of low atomic number biocompatible materials such as stainless steel or titanium which substantially do not absorb X-rays. The isotope is coated on a rod shaped carrier made of similar X-ray transparent (e.g. low Z) material and is placed inside the capsule cylinder. The ends of the capsule cylinder are closed by swaging or spinning and soldering or welding. According to a preferred embodiment, Lawrence places a radiopaque marker inside the seed. In one embodiment, the marker is a wire embedded inside the carrier rod. The wire is made of high atomic number material such as gold or tungsten which absorb X-rays.
Kubiatowicz made a minor improvement in the basic Lawrence design by providing that the entire isotope carrier be made of radiopaque material such as silver. Kubiatowicz recognized that since the isotope was carried on the entire outer surface of the carrier, there was no need to make the carrier body X-ray transparent as suggested by Lawrence. The larger radiopaque carrier body described by Kubiatowicz makes the seeds easier to see with X-ray or fluoroscopic examination. Thus, the seeds may be placed more accurately at or around the treatment site.
The Coniglione patent provided a tubular seed adapted for longitudinally receiving suture material to facilitate securing the seed at an implant site. The seed optionally includes a radiopaque band centrally located on the outer surface of the seed, and the radioactive isotope either extends over the entire outer surface of the seed, including over the band, or is coated on the outer surface of the seed from the ends of the seed to areas adjacent the edges of the band.
Despite the fact that radioactive therapeutic seeds have been in use for over thirty years and despite the several significant improvements made in these seeds, many concerns still exist regarding their design. In certain instances where radioactive seed therapy is prescribed for a patient, a physician may desire to have different levels of radioactivity at various locations within the treatment site and thereafter monitor how the tissue is affected by seeds radiating particular levels of radiation. Or the physician may want to implant seeds having isotopes with different half lives, thereby permitting selected locations to receive radiation over a longer period of time, and monitor which seeds are active. However, according to the known seed designs and methodology, it is not possible to distinguish one seed from another after implantation based upon a seed marker with an imaging systems, e.g., X-ray. Due to the indistinguishability of the seeds, implantation of seeds having different respective properties at a single site of treatment is not purposefully performed.
It is therefore an object of the invention to provide a system of radioactive therapeutic seeds in which at least one of the therapeutic seeds has a different level of radioactivity relative to other seeds.
It is also an object of the invention to provide a system of radioactive therapeutic seeds in which at least one of the therapeutic seeds has a marker which is different relative to other seeds.
It is another object of the invention to provide radioactive therapeutic seeds in which at least one of the therapeutic seeds has a different level of radioactivity and/or different half-life relative to other seeds and the marker in the at least one therapeutic seed indicates the different level of radioactivity and/or half-life relative to the other seeds.
It is an additional object of the invention to provide radioactive therapeutic seeds in which different seeds are provided with markers of different size which indicate their respective levels of radioactivity or half-life.
It is yet another object of the invention to provide a radioactive therapeutic seed which is adapted to receive markers of various lengths by a physician just prior to insertion.
It is yet a further object of the invention to provide a radioactive therapeutic seed which is adapted to have a marker which can be selectively configured by a physician just prior to insertion.
In accord with these objects which will be discussed in detail below, the radioactive therapeutic seeds of the present invention include a carrier structure bearing a radioactive isotope and a radiopaque marker.
According to a first embodiment of the invention, the isotope bearing structure may be one or more radiolucent particles, preferably made from titanium, aluminum or glass, and preferably spherically shaped. The particles are provided with a thin coating of silver to facilitate the adhesion of the isotope thereto. Also provided is a relatively thick tubular titanium plug having an axial first radiopaque marker therein. The plug preferably includes a circumferential ridge against which the open ends of the two halves of the capsule are butt against and welded thereto. The plug and the marker are provided with a transverse bore accessible from the exterior of the seed. A second marker may be positioned in the bore, thereby radiographically distinguishing a seed provided with the second marker relative to a seed not provided with the second marker; i.e., a seed provided with solely the first marker will have a broken linear radiographic image, while a seed provided with both the first and second markers will have a cross-shaped radiographic image. A plurality of seeds as described may be provided in a system which includes a plurality of seeds and a plurality of second markers for selective insertion into the seeds by a physician. Alternatively, the seeds may be provided to the physician already divided into groups which are distinguishably radiographically marked.
According to a second embodiment of the invention, a seed includes an isotope bearing structure, which is preferably a pair of silver tubes having an interior surface on which the isotope is provided. One silver tube is positioned in each half of the capsule, and the halves of the capsule are welded about a relatively thick centrally located tubular titanium plug. The plug is preferably provided with a first radiopaque marker therein. The plug and the marker are provided with a transverse bore accessible from the exterior of the seed, and the bore may be provided with a second marker, as described above. In addition, the isotope bearing tube is preferably smaller than the interior of each half of the capsule, and a spacer is preferably provided in each half of the capsule between the tube and the plug to prevent relative movement of the tube within the capsule.
According to a third embodiment of the invention, the isotope is deposited on the outer surface of a hollow radiolucent tube. A radiopaque band may be centrally located on the outer surface of the seed, and the radioactive isotope may then either extend over the entire outer surface of the seed, including over the band, or may be coated on the outer surface of the seed from the ends of the seed to areas adjacent the edges of the band. A biologically-compatible, radiolucent, surface-sealing layer seals the external surface of the tube. A radiopaque marker wire is positioned in the hollow of the tube, and where the seed is provided with a radiopaque band, the marker wire is preferably of a length different than the band. It will be appreciated that in a system of seeds according this embodiment, seeds may be radiographically distinguished from one another by providing seeds with marker wires of different lengths.
According to a fourth embodiment of the invention, the seed includes an element on which the isotope is provided, and a marker which can be varied in size or shape by application of energy to the seed.
According to fifth through ninth embodiments of the invention, the seed includes a substantially cylindrical outer member, and a substantially cylindrical inner member provided within the outer member and having two large diameter portions and a relatively smaller diameter portion therebetween. A marker which permits at least one of a radiographic and a MRI image is longitudinally disposed within the inner member, and a radioactive isotope is carried on the small diameter portion of the inner member. In each embodiment, the marker may be drilled to a smaller size, e.g., with a laser drill or mechanical drill, to radiographically distinguish the drilled marker from a non-drilled marker.
Each embodiment permits at least two groups of seeds to be radiographically distinguished from one another by the use of differing marker configurations. Each embodiment is further capable of being selectively marked by the physician prior to implantation of the seeds, or by the manufacturer for delivery to the physician in radiographically distinguishable sets. As a result, seeds having different levels of radiation emission can be distinguished in vivo and their effect monitored by the physician.